Redirecting flow to reduce disturbances upon an actuator arm or head-gimbal assembly of a disc drive

ABSTRACT

A flow-induced disturbance upon an actuator arm is reduced. A gas flow generated by a rotation of a disc is received and passed along a surface. The surface is mechanically isolated from the actuator arm. The surface redirects the received flow to include a substantial inward radial component so as to be better aligned along a leading edge of the actuator arm.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to United States ProvisionalApplication No. 60/193,686 filed Mar. 31, 2000.

FIELD OF THE INVENTION

[0002] This invention relates generally to the field of data handlingdevices, and more particularly to directing gas flow withinelectromechanical data storage devices to permit more accuratetransducer positioning.

BACKGROUND OF THE INVENTION

[0003] Computers commonly use disc drives or tape drives to store largeamounts of data in a form that can be readily accessed by a user. Atypical disc drive generally includes a stack of vertically spacedmagnetic discs that are rotated at high speed by a spindle motor. Thesurface of each disc is divided into a series of concentric, radiallyspaced data tracks in which the data are stored in the form of magneticflux transitions. Each data track is divided into a number of datasectors that store data blocks of a fixed size.

[0004] Data are typically stored and accessed on the discs by an arrayof read/write heads mounted to a rotary actuator assembly, or “E-block.”Typically, the E-block includes a plurality of actuator arms whichproject outwardly from an actuator body to form a stack of verticallyspaced actuator arms. The stacked discs and arms are configured so thatthe surfaces of the stacked discs are accessible to the heads mounted onthe complementary stack of actuator arms.

[0005] Head wires included on the E-block conduct electrical signalsfrom the heads to a flex circuit, typically, which in turn conducts theelectrical signals to a flex circuit bracket mounted to a disc drivebasedeck. For a discussion of some modern E-block assembly techniques,see U.S. Pat. No. 5,404,636 entitled “Method of Assembling a Disk DriveActuator” issued Apr. 11, 1995 to Frederick M. Stefansky et al., andassigned to the assignee of the present invention.

[0006] The actuator body pivots about a cartridge bearing assembly whichis mounted to the disc drive housing at a position closely adjacent theouter extreme of the discs. The actuator assembly includes a voice coilmotor which enables the actuator arms and the heads attached thereto tobe rotated about the cartridge bearing assembly so that the arms movehorizontally (i.e. in a plane parallel to the surfaces of the discs) toselectively position a head adjacent to a preselected data track.

[0007] The voice coil motor includes a coil mounted radially outwardlyfrom the cartridge bearing assembly, the coil being immersed in themagnetic field of a magnetic circuit of the voice coil motor. Themagnetic circuit comprises one or more permanent magnets andmagnetically permeable pole pieces. When current is passed through thecoil, an electromagnetic field is established which interacts with themagnetic field of the magnetic circuit so that the coil moves inaccordance with the well-known Lorentz relationship. As the coil moves,the actuator body pivots about the pivot shaft and the heads move acrossthe disc surfaces.

[0008] Each of the heads is mounted to an actuator arm by a flexurewhich attaches to the end of the actuator arm. Each head includes aninteractive element such as a magnetic transducer which either sensesthe magnetic transitions on a selected data track to read the datastored on the track, or transmits an electrical signal that inducesmagnetic transitions on the selected data track to write data to thedata track. Air currents are caused by the high speed rotation of thediscs. A slider assembly included on each head has an air bearingsurface which interacts with the air currents to cause the head to flyat a short distance above the data tracks on the disc surface.

[0009] There is a generally recognized trend in the industry to increasetrack density, making more and more accurate track following necessary.At the same time, increasing disc rotation speeds have resulted in moreand more noise energy being transferred to each arm and head-gimbalassembly by wind. This acts as a disturbance having energy distributedacross a wide spectrum of frequencies. This makes accurate trackfollowing difficult, especially when it includes significant energy atany of the resonance frequencies of the arms. Thus, there is a need foran improved technique for reducing wind-induced disturbances upon armsand head-gimbal assemblies of the disc drive.

[0010] The present invention provides a solution to this and otherproblems, and offers other advantages over the prior art.

SUMMARY OF INVENTION

[0011] The present invention is a method of reducing a flow-induceddisturbance on an actuator arm of a disc drive. It includes a step ofreceiving a gas flow generated by a rotation of a first disc of the discdrive. The received flow is guided along a surface mechanically isolatedfrom the actuator arm. The surface redirects the received flow toinclude a substantial inward radial component so as to be better alignedalong a leading edge of the actuator arm, thereby exerting less forceupon it.

[0012] Optionally, the guiding also increases the turbulence of the flowto a moderate degree just upstream from the actuator, which is believedto make it less likely for structural resonances to develop fully. Theseand other features and benefits will become apparent upon a review ofthe following figures and their accompanying detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 shows a disc drive configured to implement the presentinvention.

[0014]FIG. 2 shows a flowchart of a method of the present invention.

[0015]FIG. 3 shows a top view of the disc drive of FIG. 1, showing inmore detail how it can perform the method of FIG. 2.

[0016]FIG. 4 plots a disturbance indicator as a function of actuatorposition for various heads, with and without the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Referring to the drawings in general, and more particularly toFIG. 1, shown there is a disc drive 100 configured to implement thepresent invention. Disc drive 100 includes a housing 150 containingseveral discs 140 in a stack arranged for co-rotation in a conventionalmanner. Preferably, the discs 140 are each at least 50 mils thick. Thecover for the housing (not shown) provides a conventional sealedenvironment. The top and bottom flat surfaces of each disc 140 eachinclude many thousands of circular tracks 132 containing data. A rotaryactuator 110 supports several transducer heads 160 each supported on arespective arm 111 adjacent a respective surface of a disc 140. Aconventional voice coil motor 130 controls the position of the actuator110 so that a selected one of the heads 160 is positioned above aselected track 132. Once the head 160 is following the selected track132, data can be retrieved from or written to the track 132 via a flexconnector 164 through which data signals flow.

[0018] The discs 140 spin, counterclockwise as shown, at severalthousand revolutions per minute. This causes a wind of hundreds of feetper second to bear upon the leading edge 176 of each actuator arm 111,sometimes causing a flow-induced disturbance upon the actuator arm 111that makes track following difficult. In prior art configurations, airtraveling substantially tangent to the disc circumference could collidewith a leading edge of an actuator at angles within 30 degrees of thenormal, especially when track following at the innermost track.

[0019] According to the present invention, a wind-induced disturbance isreduced by redirecting a portion of the flow inward so that the wind isbetter aligned along a leading edge of the actuator arm. In theembodiment of FIG. 1, this is accomplished by a J-shaped channel 172having a uniform width 323 and depth 123. Put another way, so that thechannel 172 can accommodate a significant flow, all of the crosssections along the channel have a width 323 greater than R/100, where Ris the nominal radius 311 of the disc. Most importantly for presentpurposes, the J-shaped channel 172 includes a redirecting surface 173that is mechanically isolated from the actuator arm.

[0020] As used herein, a surface is “mechanically isolated” from anactuator arm if the surface is only coupled to the actuator arm throughthe actuator body. Suitable isolation may be obtained by providing thesurface on a structure coupled to the housing 150 or to the body of theactuator 110, for example.

[0021]FIG. 2 shows a method 200 of the present invention comprisingsteps 205 through 235. A flow traveling along an edge of a rotating discis received 210 and redirected toward the inner diameter of the disc.The redirected flow is then combined with a circumferential flowtraveling along an edge of the disc 225. The combined flow (shown inregion 174 of FIG. 1) then has a substantial inward radial component.(As used herein, a flow direction has a “substantial” radial componentif the flow direction differs from the tangent direction by about 2degrees or more.)

[0022] While the just-combined flow 346 still has a substantial inwardradial component, it is passed along the leading edge of each actuatorarm so as to reduce a windage-induced disturbance. The combined flow canoptionally be permitted to laminarize while the disc carries the flowthrough about 10-90 degrees of its rotation.

[0023]FIG. 3 shows a top view of the disc drive 100 of FIG. 1,highlighting how the disc drive 100 of FIG. 1 can perform the method ofFIG. 2. The axis of rotation 374 of the actuator is shown, as is theaxis of rotation 376 of the disc stack. Radius 311 is shown explicitly,and radius 355 is shown in part, marking the leading side of thecombined flow region 174 (of FIG. 1). Within the half-circle upstreamfrom (i.e. below) radius 355 near the discs, it can be assumed forpresent purposes that all of the air travels substantially tangent tothe rotation. For example, flow 345 flows in a substantially tangentdirection. As used herein, “substantially tangent” means within twodegrees of being tangent to a centered about axis 376. (In ordinary discdrives, flow very near each disc will actually have a somewhat moreoutward direction than flow mid-way between successive discs, acentrifugal effect.)

[0024] An air flow 342 traveling along the circumference of a disc 140is initially received at the inlet of the channel 172. The inner radius321 and the outer radius 322 of the channel 172 have a difference equalto the inlet width 323, so that the channel maintains a nominallyconstant cross-sectional area along its J-shaped length. Encounteringthe curved wall 173, the redirected flow 343 therefore maintains anearly-constant speed even as it is expelled 344. The fastest portion ofthe expelled flow 344 is directed toward the inner diameter 361 of eachdisc 140, encountering the tangential flow 345 at an angle 327 of about90 degrees. In preferred embodiments, the area-averaged injection angle327 is at least about 30 degrees.

[0025] The combined flow 346 has a direction including a substantialinward radial component, as shown by the angle 326 departing fromtangent by several degrees. The mixed flow region 174 upstream from eachactuator arm 176 is characterized by a substantial inward flow directioncomponent. After rotating with the disc about a travel angle 328 ofabout 30 to 60 degrees, the combined flow 346 encounters the leadingedge 176. A larger travel angle will tend to laminarize thejust-combined flow 346 but decrease its inward angle 326. In preferredembodiments, most of the area of the leading edge 176 of the actuatorarm 111 comes in contact with the mixed flow 346,348 before the mixedflow travels about an angle 329 of less than 90 degrees.

[0026] As the just-combined 346 flow draws very near the leading edge176, it is redirected again. Part of the just-combined flow 346 travelsabove and below the actuator arm 176 in manner similar to that of theprior art. More importantly, part of the flow 348 travels along theleading edge 176. Because the combined flow 346 transfers less energy tothe actuator arm 111 than an ordinary tangent flow 345 would, especiallyat a resonance frequency F of the actuator arm, disc drives 100performing the present method are better able to follow tracks 132accurately.

[0027]FIG. 4 plots disturbance indicator as a function of actuatorposition 401. Actuator position 401 is expressed as a track (cylinder)number. The 0th track is at the outer diameter, and the inner diameteris numbered about 10,000. The disturbance indicator is Non-RepeatableRun Out (NRRO) expressed in microinches 402. At each of severalmeasurement cylinders, a position error signal (PES) indicates ameasured deviation from an expected radial position many times. Thesemeasurements were divided into three groups, each group being used toderive a respective mean and a standard deviation. The means eachrepresent Repeatable Run Out (RRO), which was ignored for presentpurposes. The standard deviations, expressed in microinches, wereaveraged to obtain the present indicator of NRRO 402.

[0028] The disc drive from which the data of FIG. 4 were gathered hadfive discs, each with two surfaces. The heads were conventionallynumbered 0 through 9. Before the method of the present invention wasperformed within the drive, head 0 resulted in NRRO indicator 440, head1 resulted in NRRO indicator 441, and head 5 resulted in NRRO indicator445. This reflects the fact that heads near the top and bottom discgenerally suffered worse NRRO than heads near the middle disc. It isbelieved that stationary surfaces above and below the disc stack servedto dampen the flow impinging upon the actuator arms near the top andbottom, especially those coupled to heads 0 and 9. This is supported bythe fact that the worst case NRRO was always measured near the innerdiameter (on the right side of FIG. 4) for the heads positioned betweendiscs (i.e. heads 1 through 8).

[0029] After the disc drive was reconfigured to perform the presentmethod, head 0 showed a greatly reduced indication 450 of NRRO. Heads 1and 5 also showed greatly reduced NRRO indications 451,455. For all ofthe heads positioned between discs, this improvement was more than 3%across all actuator positions 401. This is significant evidence of theimportance of the present invention, especially in view of the presentconcern that track densities are becoming too high to allow trackfollowing by existing methods.

[0030] By way of review, a first alternative embodiment of the presentinvention is a method (such as 200) of reducing a flow-induceddisturbance on an actuator arm (such as 111) of a disc drive (such as100). A gas flow (such as 342) generated by a rotating disc (such as140) is received (e.g. by step 210) and passed along a surface (such as173) mechanically isolated from the actuator arm(s). The surfaceredirects the flow to include a substantial inward radial component(e.g. by step 215). Preferably, the redirected flow (such as 344) isexpelled toward an inner diameter (such as 361) of the disc (such as140). The redirected flow (such as 344) is then combined (e.g. by step225) with a tangent flow (such as 345) so that the combined flow (suchas 346) has a net flow direction with an inward radial component (suchas 326). The combined flow (such as 346) is redirected again by theactuator arm(s) (such as 111), preferably before it travels ¼ of arevolution of the disc. The redirected flow (such as 348) along theleading edge is shown in FIG. 3. Because the just-combined flow (such as346) is better aligned with the leading edge (such as 176) of theactuator arm than a tangential flow encountering the actuator arm wouldbe, the flow-induced disturbance on the actuator arm is reduced by thepresent method.

[0031] A second alternative embodiment is a disc drive (such as 100)well-suited for performing the above method (such as 200). The discdrive has multiple discs (such as 140) and an air flow channel (such as172) positioned upstream of an actuator arm (such as 111). The channelhas a horizontal cross-section with a minimum macroscopic radius ofcurvature (such as 322) greater than R/100 so that the flow isredirected with a minimum drag-induced energy loss. The flow mayoptionally be passed along textured channel surfaces (with recessessmaller than R/1000 in depth and diameter) so as to reduce drag further.Preferably, the cross-sectional area of the channel is sufficientlyuniform along the length of the channel so that, downstream from thechannel inlet, flow speed is maintained within 50% all along the curvedchannel. Alternatively, the flow can be guided so as to remain at auniform height along the channel(s). The channel is vertically uniform(as shown in FIG. 3) so that the inward radial component of theredirected flow will be larger between the discs than above or below thestack of discs. For ease of implementation, also, the curved surface(such as 173) preferably does not extend above or below any of the majorsurfaces of the discs (such as 140).

[0032] In a third alternative embodiment, the turbulence of (most or allof the flow is increased while the flow is redirected. This increasecorresponds with an increase in the Reynolds number of the flow of atleast 5%, but should not be so large that the Reynolds number exceeds3000 as the redirected flow (such as 346) approaches the actuatorarm(s). It is believed that this controlled increase in turbulence makesit less likely for structural modes in the actuator arm(s) to developfully as the flow is redirected again by the actuator arm(s). Note thatthe depicted channel (at 172) permits this flow change without extendingthe surface over the disc(s).

[0033] It will be clear that the present invention is well adapted toattain the ends and advantages mentioned as well as those inherenttherein. While presently preferred embodiments have been described forpurposes of this disclosure, numerous changes may be made which willreadily suggest themselves to those skilled in the art and which areencompassed in the spirit of the invention disclosed and as defined inthe appended claims.

What is claimed is:
 1. A method of reducing a flow-induced disturbanceon an actuator arm of a disc drive, comprising steps of: (a) receiving agas flow generated by a rotation of a first disc of the disc drive; and(b) guiding the received flow along a surface mechanically isolated fromthe actuator arm so as to cause the flow to include a substantial inwardradial component and to be more closely aligned along a leading edge ofthe actuator arm.
 2. The method of claim 1 in which the disc drivefurther includes a second disc configured for co-rotation with the firstdisc, and in which the guiding step (b) is performed without extendingthe surface between the first and second discs.
 3. The method of claim 1further comprising a step (c) of redirecting the guided flow with theleading edge of the actuator arm before the guided flow travels ¼ of arevolution of the disc.
 4. The method of claim 1 in which the disc has anominal radius R, in which the surface has a horizontal cross-sectionwith a minimum macroscopic radius of curvature greater than R/100 sothat the guiding step (b) is performed with a minimal drag-inducedenergy loss.
 5. A method of reducing a flow-induced disturbance on anactuator arm of a disc drive, comprising steps of: (a) receiving a gasflow generated by a rotation of a first disc of the disc drive; and (b)guiding the received flow along a surface mechanically isolated from theactuator arm so as to cause the received flow to include a substantialinward radial component so as to be more closely aligned along a leadingedge of the actuator arm by directing the received flow through achannel that is stationary with respect to a housing.
 6. The method ofclaim 5 in which the disc has a nominal radius R and in which thesurface has a horizontal cross-section with a minimum macroscopic radiusof curvature greater than R/100 so that the directing step (b1) isperformed with a minimal drag-induced energy loss.
 7. The method ofclaim 5 in which the disc drive further includes a second discconfigured for co-rotation with the first disc, and in which the channelhas a vertically uniform cross section so that the radial component ofthe guided flow will be larger between the discs than above the discs.8. The method of claim 5 in which the guiding step (b) includes a step(b1) of expelling at least part of the guided flow toward an innerdiameter of the disc.
 9. The method of claim 8 in which the guiding step(b) further includes steps of: (b2) combining the expelled flow with atangent flow traveling along an edge of the disc so that the combinedflow has a net flow direction with an inward radial component; (b3)redirecting the combined flow again with the leading edge of theactuator arm before the combined flow travels ¼ of a revolution of thedisc so that the flow-induced disturbance on the actuator arm is reducedby the inward radial component of the net flow direction.
 10. The methodof claim 5 in which the flow of the receiving step (a) has a flow speedand in which the guiding step (b) includes a step (b1) of maintainingthe flow speed within 50% while the received flow remains within thechannel.
 11. The method of claim 5 in which the disc has a nominalradius R and in which a narrowest cross section along the channel has awidth greater than R/100 so that the channel can accommodate asignificant flow.
 12. A method of reducing a flow-induced disturbance onan actuator arm of a disc drive, comprising steps of: (a) receiving agas flow generated by a rotation of a first disc of the disc drive, theflow having an initial turbulence level corresponding to an initialReynolds number T.; (b) guiding the received flow along a surfacemechanically isolated from the actuator arm so as to make the flow moreturbulent and to cause the flow to include a substantial inward radialcomponent so as to be more closely aligned along a leading edge of theactuator arm; and (c) while a majority of the guided flow has a largerReynolds number>1.05T, redirecting the guided flow with the leading edgeof the actuator arm.
 13. The method of claim 12 further comprising astep (c) of redirecting the guided flow with the leading edge of theactuator arm before the guided flow travels ¼ of a revolution of thedisc.
 14. The method of claim 12 in which the disc has a nominal radiusR, in which the surface has a horizontal cross-section with a minimummacroscopic radius of curvature greater than R/100 so that the guidingstep (b) is performed with a minimal drag-induced energy loss.
 15. Themethod of claim 12 in which the disc drive further includes a seconddisc configured for co-rotation with the first disc, and in which theguiding step (b) is performed without extending the surface between thefirst and second discs.